[Dynamicpower-devel] Re: patch for omap for dpm-2.6.11 (change read_mputimer1() to sched_clock())

[Todd P. <tp...@mv...>]

Hello Amit --

> The sched_clock fucntion returns time in nanoseconds. It is defined for both
> 32K timer and MPU timer. Please let me know whether the the bitwise negation
> should be removed because I didn't see any "0 - omap_mpu_timer_read(0)".
> 
> If we want the resolution in microseconds or milliseconds, we can multiply
> the value returned by sched_clock(). Please let me know.
> 
>>From arch/arm/kernel/time.c
> 
> unsigned long long __attribute__((weak)) sched_clock(void)
> {
>         return (unsigned long long)jiffies * (1000000000 / HZ);
> }

Ah, I forgot they use nanoseconds resolution, I suppose we could convert 
to keep the units reasonable for instrumentation purposes.

Note that the above is the jiffie-based (so actually 
millisecond-resolution) default sched_clock() for ARM if a 
higher-resolution version based on board-specific timers is not provided 
(hence the "weak" attribute).  See arch/arm/mach-omap/time.c for the MPU 
Timer 1 based sched_clock for OMAPs (in recent OMAP tree).

Thanks,

-- 
Todd